Or go with a Human who is perfectly healthy and of average intelligence, and have them assigned temporarily to a Starfleet vessel where the majority of the crew is non-Human. In comparison the Human is slow (both physically and mentally), and this causes problems which the crew comments on, and the Human is shunted to the side in terms of duties and maybe even socially.
This would be the point of the story, a person who lacks the capacities of the surrounding society. In the end the Humans different abilities save the day, showing that being "lessor" is some way doesn't mean that you are so across the board.
By having the "disabled" person be the Human, the audience would be better able to put themselves into the character's shoes.